Code extracted from:

    https://gitlab.kitware.com/third-party/proj.git

at commit 41bdf05361007f8c5186f3df9944d86bb273ed13 (for/vtk).

Find/replace of:

with C++ counterparts.  Changed only vtk*.cxx files.
Didn’t touch .h or .c or any 3rd party.

Cleaning up issues with the context-items related to tranfer function editor.

+ Added support for log-mapped color-transfer function. We ensure that when
  using log-scale, the color transfer function widget also enter log-space.

+ vtkPiecewiseControlPointsItem had a bug resulting it deleting of end points
  even when told otherwise. Fixed that.

+ Added new event vtkControlPointsItem::PointsModifiedEvent which if fired when
  control points are changed making it easier for application to do something
  when the points are changed.

+ Improved the usability by adding ability to label control points.

Change-Id: If02bc1139f6ccb3d7c2198b07d10491f902bafda

Move source files from their former monolithic VTK location to their new
location in modular VTK without modification.  This preserves enough
information for "git blame -M" and "git log --follow" to connect
modularized VTK files to their original location and history.

Co-Author: Marcus D. Hanwell <marcus.hanwell@kitware.com>
Co-Author: Chris Harris <chris.harris@kitware.com>
Co-Author: Brad King <brad.king@kitware.com>
Co-Author: Nikhil Shetty <nikhil.shetty@kitware.com>

The old value 255 was not large enough when the chart is displayed with a
1024 pixel width. It was make the texture pixelated.

By default vtkScalarsToColorsItem uses the bounds defined by the transfer
function range. The user might want to use different bounds.

-You can edit control points in 2 fashions:
 If vtkControlPointsItem::StrokeMode is true, you can "draw" points while
the left mouse button is down, it will add control points under the mouse
cursor.
 If vtkControlPointsItem::StrokeMode is false, you can drag&drop existing
points. SwitchPointsMode control the behavior to follow when a point
crosses another.
In both modes, if you click the left button mouse not on a point, a point is
created under the mouse cursor.
-Add vtkCompositeControlPointsItem to mix ct function and opacity function.
It creates points for Color Transfer and Opacity
functions.Both functions will share the same control points.
-Add vtkControlPointsItem::EditPoint to control midpoint and sharpness
-Support null transfer functions in the ScalarsToColors items

-You can edit control points in 2 fashions:
 If vtkControlPointsItem::StrokeMode is true, you can "draw" points while
the left mouse button is down, it will add control points under the mouse
cursor.
 If vtkControlPointsItem::StrokeMode is false, you can drag&drop existing
points. SwitchPointsMode control the behavior to follow when a point
crosses another.
In both modes, if you click the left button mouse not on a point, a point is
created under the mouse cursor.
-Add vtkCompositeControlPointsItem to mix ct function and opacity function.
It creates points for Color Transfer and Opacity
functions.Both functions will share the same control points.
-Add vtkControlPointsItem::EditPoint to control midpoint and sharpness
-Support null transfer functions in the ScalarsToColors items

and vtkCompositeTransferFunctionItem), specially if the option
MaskAboveCurve is off.

The opacity is overwritten by MapScalarsThroughTable2

They can be added into any vtkChartXY. Their size depend on the
vtkScalarsToColors (vtkLookupTable or vtkColorTransferFunction) range.